feat: a release catalogue from MusicBrainz; request search asks it directly (M502 #5519)

Minstrel keeps its own record of what artists have released, read from
MusicBrainz, so the wanted list, search and import no longer need Lidarr.

- internal/musicbrainz: searches (artists, release groups, recordings) and
  browses (an artist's release groups; a group's releases with track lists).
  One process-wide pacer at 1.1s, shared with tag enrichment, because
  MusicBrainz's limit is per address. A 503 throttle is retried.
- Migration 0080: mb_artists, mb_release_groups, mb_artist_release_groups
  (a collaboration belongs to each credited artist), mb_releases,
  mb_release_tracks.
- internal/catalogue: Discography and Releases serve the held copy and
  re-read it when older than 7 or 30 days. An unreachable MusicBrainz
  serves the stale copy, marked. An hourly pass re-reads due artists.
- Art for what isn't held comes through /api/catalogue/art from the
  enabled cover-art sources (Cover Art Archive by release group, then the
  name-based sources) and is kept on disk, so the browser never fetches a
  third-party host. A miss is a 404 and the card shows its icon.
- Request search moves from /api/lidarr/search to /api/catalogue/search,
  with the same response shape. Albums are release groups, and "in
  library" matches albums.release_group_mbid. A 10-minute cache absorbs
  search-as-you-type. Discover suggestions point at the art endpoint
  instead of looking up Lidarr.
- Android calls the new path and loads Discover art through ServerImage.
  Installed builds older than this one lose Discover search until they
  update (no compatibility path, rule 22).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/dbtest/reset.go

@@ -103,6 +103,11 @@ var dataTables = []string{
 	"user_notification_prefs",
 	"user_notification_email_state", // #5346
 	"acquisition_services",          // M502 #5518
+	"mb_release_tracks",             // M502 #5519
+	"mb_releases",                   // M502 #5519
+	"mb_artist_release_groups",      // M502 #5519
+	"mb_release_groups",             // M502 #5519
+	"mb_artists",                    // M502 #5519
 	"tracks",
 	"albums",
 	"artists",